Kiribati
Kiribati is a small nation made up of lots of tiny islands deep in the pacific, north-east of Australia and New Zealand. If you look at a map that shows time zones, it will stand out like a sore thumb for it juts out massively, since its island territories should straddle 3 time zones but instead all exist in one timezone. This also means, in their case, they are a day ahead of their immediate neighbours since they are on the east side of the date line when geographically they should be on the west side.
This is actually a very recent change compared to most time zone irregularities, since it was done in 1995 to sync up their working days with the much larger economies of New Zealand and Australia.